Okay, i picked an F-14 Tomcat and although it works i am not familiar with this era.
After turning it off and then back on some errors popped up. Check or adjust switches 30,31,32 which are the lower, middle and upper ramps. Besides that, quite often the balls get lost in the center playfield locks. But the switches there seem okay when tested. So when a second ball lands on it, the machine then waits a minute and kicks out all of the locked balls wherever they are on the playfield.
The switches 30,31 and 32 were fine last night after i set it up for the first time it is only today that they check as an error.

Where should i start?

bad connector on the underside of playfield.....causing intermittent breaks in signal from the 3 switches..........which accounts for all of the problems, i think. Moved and reseated the connectors a bit and the switches registered correctly. It may be time to replace the connector.